AC-to-DC power converter with improved power factor and overvoltage suppression

Abstract

An AC-to-DC power conversion by connecting GTO elements to the positive arms of a three-phase full wave bridge circuit and by repeating the mode of supplying power to a load from an AC power supply by controlling the GTO elements, and the mode of making the current flowing to the load flow back at the time of interruption of the power supply mode, when the power supply mode and the flow-back mode are switched over, overvoltage at the time of the switching is suppressed by simultaneously causing the power supply and flow-back currents to flow.

We claim: 
     
       1. A power converter apparatus comprising an AC power supply, a DC load and controllable switching means connected across said AC power supply and said DC load and provided with a current-breaking function for alternately repeating the mode of rectifying said AC power and supplying power to said DC load and the mode of making the current flowing to said DC load flow back, pulse generating means for generating a gate-on pulse for one of the power supply mode and the flow-back mode and a gate-off pulse for one of the flow-back mode and the power supply mode, said power converter apparatus being futher provided with gate control means response to the gate pulses from said pulse generating means for controlling said controllable switching means so that said power supply current and said flow-back current simultaneously flow at the time of said power supply to flow-back-mode switching. 
     
     
       2. A power converter apparatus as claimed in claim 1, wherein said gate control means controls said controllable switching means in such a way that said flow-back current is made to rise during a period of time that said power supply current is attenuating, whereby an overvoltage occurring at the time of the mode switching is suppressed and a breakdown of the switching means due to the overvoltage is prevented. 
     
     
       3. A power converter apparatus as claimed in claim 1, wherein said gate control means controls said controllable switching means in such a manner that said power supply current is allowed to rise during a period of time that said flow-back current is attenuating, whereby an overvoltage occurring at the time of the mode switching is suppressed and a breakdown of the switching means due to the overvoltage is prevented. 
     
     
       4. A power converter apparatus as claimed in claim 1, wherein said gate control means enables said controllable switching means forming said flow-back mode to hold an on state while said controllable switching means forming said power supply mode is holding an off state. 
     
     
       5. A power converter apparatus as claimed in claim 1, wherein said gate control means enables simultaneous application of the gate-off pulse and the gate-on pulse for said controllable switching means forming said power supply mode and said flow-back mode, respectively. 
     
     
       6. A power converter apparatus as claimed in claim 1, wherein said gate control means enables said controllable switching means forming said power supply mode to hold an on state while said switching means forming said flow-back mode is holding an off state. 
     
     
       7. A power converter apparatus as claimed in claim 6, wherein said gate control means enables simultaneous application of the gate-off pulse and the gate-on pulse for said controllable switching means forming said flow-back mode and said power supply mode, respectively. 
     
     
       8. A power converter apparatus as claimed in claim 1, wherein a full wave bridge rectifier circuit is connected across said AC power supply and said DC load, said controllable switching means forming each of a plurality of arms of said full wave bridge circuit. 
     
     
       9. A power converter apparatus as claimed in claim 8, wherein said controllable swithcing means form the positive arm of said full wave bridge circuit, whereas thyristors form the negative arms. 
     
     
       10. A power converter apparatus as claimed in claim 8, wherein said power supply mode is formed by making any of said controllable switching means of said full wave bridge circuit conduct, whereas said flow-back mode is formed by making said controllable switching means forming arms forming a closed loop with said DC load conduct. 
     
     
       11. A power converter apparatus as claimed in claim 10, wherein said gate control means operates to overlap a terminating point of a period during which said controllable switching means forming said power supply mode is conducting and a starting point of a period during which said controllable switching means forming said flowback mode is conducting. 
     
     
       12. A power converter apparatus as claimed in claim 10, wherein said gate control means operates to overlap a terminating point of a period during which said controllable switching means forming said flow-back mode is conducting and a starting point of a period during which said controllable switching means forming said power supply mode is conducting. 
     
     
       13. A power converter apparatus comprising an AC power source, a DC load, and a plurality of controllable switching means connected between said AC power source and said DC load and each having an electric current cut-off function for enabling a switching in accordance with gate pulses cyclically between a power-supply mode in which the current from said AC power source is rectified and supplied to said DC load and a flow-back mode in which the electric current in said DC load is fed back, pulse generating means for generating a gate-on pulse for said flow-back mode before the generation of a gate-off pulse for said power-supply mode, and means for supplying gate pulses to said controllable switching means in response to the generated pulses from said pulse generating means for enabling power-supply current and flow-back current to simultaneously flow at a time of mode switching, whereby an overvoltage occurring at the time of the mode switching is suppressed and a breakdown of the controllable switching means due to the overvoltage is prevented. 
     
     
       14. A power converter apparatus as claimed in claim 13, wherein a full wave bridge circuit is connected across said AC power supply and said DC load, said controllable switching means forming each of a plurality of arms of said full wave bridge circuit. 
     
     
       15. A power converter apparatus as claimed in claim 14, wherein said controllable switching means form the positive arm of said full wave bridge circuit, whereas thyristors are connected to the negative arms of said full wave bridge circuit. 
     
     
       16. A power converter apparatus as claimed in claim 14, wherein said power-supply mode is formed by making any of said controllable switching means forming said full wave bridge circuit conduct, whereas said flow-back mode is formed by making said controllable switching means forming arms forming a closed loop with said DC load conduct. 
     
     
       17. A power converter apparatus comprising an AC power source, a DC load, and a plurality of controllable switching means connected between said AC power source and said DC load and each having an electric current cut-off function for enabling switching in accordance with gate pulses cyclically between a power-supply mode in which the current from said AC power source is rectified and supplied to said DC load and a flow-back mode in which the electric current in said DC load is fed back, pulse generating means for generating a gate-on pulse for said power-supply mode before the generation of a gate-off pulse for said flow-back mode, and means for supplying gate pulses to said controllable switching means in response to the generated pulses from said pulse generation means for enabling power-supply current and flow-back current to simultaneously flow at a time of mode switching, whereby an overvoltage occurring at the time of the mode switching is suppressed and a breakdown of the controllable switching means due to the overvoltage is prevented. 
     
     
       18. A power converter apparatus as claimed in claim 17, wherein a full wave bridge circuit is connected across said AC power supply and said DC load, said controllable switching means forming to each of a plurality of arms of said full wave bridge circuit. 
     
     
       19. A power converter apparatus as claimed in claim 18, wherein said switching means forming the positive arm of said full wave bridge circuit, whereas thyristors forming the negative arms of said controllable full wave bridge circuit. 
     
     
       20. A power converter apparatus as claimed in claim 18, wherein said power-supply mode is formed by making any of said controllable switching means forming said full wave bridge circuit conduct, whereas said flow-back mode is formed by making said controllable switching means forming arms forming a closed loop with said DC load conduct.